Halftone phase shift mask blank and halftone phase shift mask

ABSTRACT

A halftone phase shift mask blank comprising a transparent substrate and a halftone phase shift film thereon is provided. The halftone phase shift film includes at least one layer composed of a silicon base material having a transition metal content≦3 at %, a Si+N+O content≧90 at %, a Si content of 30-70 at %, a N+O content of 30-60 at %, and an O content≦30 at %, and having a sheet resistance≦10 13 /Ω/□. The halftone phase shift film undergoes minimal pattern size variation degradation upon exposure to sub-200 nm radiation, and has chemical resistance and improved processability.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2016-190050 filed in Japan on Sep. 28, 2016,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a halftone phase shift mask blank and ahalftone phase shift mask for use in the microfabrication ofsemiconductor integrated circuits or the like.

BACKGROUND ART

In the field of semiconductor technology, research and developmentefforts are continued for further miniaturization of pattern features.Recently, as advances including miniaturization of circuit patterns,thinning of interconnect patterns and miniaturization of contact holepatterns for connection between cell-constituting layers are in progressto comply with higher integration density of LSIs, there is anincreasing demand for the micropatterning technology. Accordingly, inconjunction with the technology for manufacturing photomasks used in theexposure step of the photolithographic microfabrication process, it isdesired to have a technique of forming a more fine and accurate circuitpattern or mask pattern.

In general, reduction projection is employed when patterns are formed onsemiconductor substrates by photolithography. Thus the size of patternfeatures formed on a photomask is about 4 times the size of patternfeatures formed on a semiconductor substrate. In the currentphotolithography technology, the size of circuit patterns printed issignificantly smaller than the wavelength of light used for exposure.Therefore, if a photomask pattern is formed simply by multiplying thesize of circuit pattern 4 times, the desired pattern is not transferredto a resist film on a semiconductor substrate due to opticalinterference and other effects during exposure.

Sometimes, optical interference and other effects during exposure aremitigated by forming the pattern on a photomask to a more complex shapethan the actual circuit pattern. Such a complex pattern shape may bedesigned, for example, by incorporating optical proximity correction(OPC) into the actual circuit pattern. Also, attempts are made to applythe resolution enhancement technology (RET) such as modifiedillumination, immersion lithography or double exposure (or doublepatterning) lithography, to meet the demand for miniaturization andhigher accuracy of patterns.

The phase shift method is used as one of the RET. The phase shift methodis by forming a pattern of film capable of phase reversal ofapproximately 180 degrees on a photomask, such that contrast may beimproved by utilizing optical interference. One of the photomasksadapted for the phase shift method is a halftone phase shift mask.Typically, the halftone phase shift mask includes a substrate of quartzor similar material which is transparent to exposure light, and a maskpattern of halftone phase shift film formed on the substrate, capable ofproviding a phase shift of approximately 180 degrees and having aninsufficient transmittance to contribute to pattern formation. As thehalftone phase shift mask, Patent Document 1 (JP-A H07-140635) proposesa mask having a halftone phase shift film of molybdenum silicide oxide(MoSiO) or molybdenum silicide oxynitride (MoSiON).

For the purpose of forming finer images by photolithography, light ofshorter wavelength is used as the light source. In the currently mostadvanced stage of lithography process, the exposure light source hasmade a transition from KrF excimer laser (248 nm) to ArF excimer laser(193 nm). The lithography using ArF excimer laser light of greaterenergy was found to cause damages to the mask, which were not observedwith KrF excimer laser light. One problem is that on continuous use ofthe photomask, foreign matter-like growth defects form on the photomask.These growth defects are also known as “haze”. The source of hazeformation was formerly believed to reside in the growth of ammoniumsulfate crystals on the mask pattern surface. It is currently believedthat organic matter participates in haze formation as well.

Some approaches are known to overcome the haze problem. With respect tothe growth defects formed on the photomask upon long-term irradiation ofArF excimer laser light, for example, Patent Document 2 (JP-A2008-276002) describes that if the photomask is cleaned at apredetermined stage, then it can be continuously used.

As the exposure dose of ArF excimer laser light irradiated for patterntransfer increases, the photomask is given damage different from haze;and the size of the mask pattern changes in accordance with thecumulative irradiation energy dose, as reported in Non-Patent Document 1(Thomas Faure et al., “Characterization of binary mask and attenuatedphase shift mask blanks for 32 nm mask fabrication,” Proc. of SPIE, vol.7122, pp 712209-1 to 712209-12). This problem is that as the cumulativeirradiation energy dose increases during long-term irradiation of ArFexcimer laser light, a layer of a substance which is considered to be anoxide of the pattern material grows outside the film pattern, wherebythe pattern width changes. It is also reported that the mask oncedamaged cannot be restored by cleaning with AMP (aqueousammonia/hydrogen peroxide) as used in the above-mentioned haze removalor with SPM (sulfuric acid/hydrogen peroxide). It is believed that thedamage source is utterly different.

Non-Patent Document 1 points out that upon exposure of a circuit patternthrough a halftone phase shift mask which is the mask technology usefulin expanding the depth of focus, substantial degradation is induced bypattern size variation resulting from alteration of a transitionmetal/silicon base material film such as MoSi base material film byirradiation of ArF excimer laser light (this degradation is referred toas “pattern size variation degradation”). Then, in order to use anexpensive photomask over a long period of time, it is necessary toaddress the pattern size variation degradation by irradiation of ArFexcimer laser light.

CITATION LIST

-   -   Patent Document 1: JP-A H07-140635    -   Patent Document 2: JP-A 2008-276002 (U.S. Pat. No. 7,941,767)    -   Patent Document 3: JP-A 2004-133029    -   Patent Document 4: JP-A 2007-033469    -   Patent Document 5: JP-A 2007-233179    -   Patent Document 6: JP-A 2007-241065    -   Non-Patent Document 1: Thomas Faure et al., “Characterization of        binary mask and attenuated phase shift mask blanks for 32 nm        mask fabrication,” Proc. of SPIE, vol. 7122, pp 712209-1 to        712209-12

SUMMARY OF INVENTION

On use of a photomask blank in the photomask producing process, ifforeign deposits are on the photomask blank, they cause defects to thepattern. To remove foreign deposits, the photomask blank is cleaned manytimes during the photomask producing process. Further, when thephotomask thus produced is used in the photolithography process, thephotomask is also repeatedly cleaned even if the photomask itself isfree of pattern defects, for the reason that if foreign deposits settleon the photomask during the photolithography process, a semiconductorsubstrate which is patterned using that photomask eventually bearspattern-transfer failures.

For removing foreign deposits from the photomask blank or photomask,chemical cleaning is applied in most cases, using SPM, ozone water orAMP. SPM is a sulfuric acid/hydrogen peroxide mixture which is acleaning agent having strong oxidizing action. Ozone water is waterhaving ozone dissolved therein and used as a replacement of SPM. AMP isan aqueous ammonia/hydrogen peroxide mixture. When the mask blank ormask having organic foreign deposits on its surface is immersed in theAMP cleaning liquid, the organic foreign deposits are liberated andremoved from the surface under the dissolving action of ammonia and theoxidizing action of hydrogen peroxide.

Although the chemical cleaning with such chemical liquid is necessaryfor removing foreign deposits such as particles and contaminants on thephotomask blank or photomask, the chemical cleaning can damage theoptical film such as halftone phase shift film on the photomask blank orphotomask. For example, if the surface of an optical film is altered bychemical cleaning, the optical properties that the film originallypossesses can be changed. In addition, chemical cleaning of thephotomask blank or photomask is repeatedly carried out. It is thusnecessary to minimize any property change (e.g., phase shift change) ofthe optical film (e.g., halftone phase shift film) during every cleaningstep.

As pointed out in Non-Patent Document 1, the pattern size variationdegradation by irradiation of short wavelength light, typically ArFexcimer laser light does scarcely occur when light is irradiated in adry air atmosphere. Exposure in a dry air atmosphere is regarded as anew approach for inhibiting the pattern size variation degradation.However, the control of a dry air atmosphere adds an extra unit to theexposure system and gives rise to electrostatic and other problems to bemanaged, leading to an increased expense. Under the circumstances, it isnecessary to enable long-term exposure in a common atmosphere that doesnot need complete removal of humidity (typically having a humidity ofaround 45%).

The photomasks used in the lithography using ArF excimer laser light aslight source include halftone phase shift masks having a halftone phaseshift film of a silicon base material containing a transition metal,typically molybdenum. This transition metal/silicon base material ismainly composed of a transition metal and silicon, and further containsoxygen and/or nitrogen as light element (e.g., Patent Document 1).Suitable transition metals used include Mo, Zr, Ta, W, and Ti. Amongothers, Mo is most often used (e.g., Patent Document 1). Sometimes asecond transition metal is added (e.g., Patent Document 3). For thelight-shielding film, silicon base materials containing a transitionmetal, typically molybdenum are also used. However, when a photomaskusing such transition metal-containing silicon base material is exposedto a large dose of high-energy radiation, the mask undergoes significantpattern size variation degradation by irradiation of high-energyradiation. Then the service lifetime of the photomask is shorter thanthe requirement.

It is a serious problem that when a photomask pattern on a halftonephase shift mask is irradiated with short-wavelength light, typicallyArF excimer laser light, the photomask pattern for exposure experiencesa variation of line width, that is, “pattern size variationdegradation.” The permissible threshold of pattern width differs withthe type of photomask pattern, especially the pattern rule appliedthereto. If variations are small, the mask may be further used bycorrecting the exposure conditions and resetting the irradiationconditions of an exposure system. For example, in the lithography forforming semiconductor circuits complying with the pattern rule of 22 nm,the variation of mask pattern line width must fall within approximately±5 nm. However, if a pattern width variation is large, there is apossibility that the variation has an in-plane distribution on thephotomask. Also in the further miniaturization technology, an auxiliarypattern having an ultrafine size of less than 100 nm is formed on themask. For the purpose of pattern miniaturization on these masks and fromthe aspect of an increase of mask processing cost by complication ofmask pattern, there is a need for a halftone phase shift mask film whichexperiences minimal pattern size variation degradation and allows forrepeated exposure.

Suitable films meeting such requirements include a film of a transitionmetal-free, silicon base material such as a film consisting of siliconand nitrogen and a film consisting of silicon, nitrogen and oxygen.Although these films are effective for improving chemical resistance andpattern size variation degradation, they suffer from a slow dry etchingrate and poor processability.

An object of the invention is to provide a halftone phase shift maskblank and halftone phase shift mask having a halftone phase shift filmwhich upon patternwise exposure using short high-energy radiation ofwavelength up to 200 nm, typically ArF excimer laser light, even in thecase of an increased cumulative irradiation energy dose, is minimized inpattern size variation degradation resulting from alteration of filmproperty by light irradiation and which is chemically resistant andeffectively processable.

Aiming to develop a halftone phase shift film having a minimized patternsize variation degradation upon exposure to ArF excimer laser light andchemical resistance, the inventors made a study on a film consisting ofsilicon and nitrogen and a film consisting of silicon, nitrogen andoxygen as the halftone phase shift film of transition metal-free siliconbase material. Although these halftone phase shift films are dryetchable with fluorine base gas, their processability is poor because ofa slow dry etching rate.

Then a study was continued on halftone phase shift films. It has beenfound that using a silicon base material comprising essentially atransition metal, silicon and nitrogen and optionally oxygen, having atransition metal content of up to 3 at %, a total content of silicon,nitrogen and oxygen of at least 90 at %, a silicon content of 30 to 70at %, a total content of nitrogen and oxygen of 30 to 60 at %, and anoxygen content of up to 30 at %, there can be formed a halftone phaseshift film having equivalent pattern size variation degradation withrespect to light of wavelength up to 200 nm and equivalent chemicalresistance as compared with transition metal-free silicon basematerials, a high etching rate during fluorine gas dry etching, andimproved processability over transition metal-free silicon basematerials.

Accordingly, in one aspect, the invention provides a halftone phaseshift mask blank comprising a transparent substrate and a halftone phaseshift film thereon having a phase shift of 150° to 200° and atransmittance of 3% to 30% with respect to light of wavelength up to 200nm. The halftone phase shift film is a single layer or a multilayerfilm, and is composed of a silicon base material comprising essentiallya transition metal, silicon and nitrogen and optionally oxygen. Thehalftone phase shift film includes at least one layer (A) composed of asilicon base material having a transition metal content of up to 3 at %,a total content of silicon, nitrogen and oxygen of at least 90 at %, asilicon content of 30 to 70 at %, a total content of nitrogen and oxygenof 30 to 60 at %, and an oxygen content of up to 30 at %, and having asheet resistance of up to 10¹³ Ω/□.

Typically, the transition metal contains molybdenum.

In a preferred embodiment, the layer (A) is compositionally graded suchthat the concentration of some or all constituent elements continuouslyvaries in thickness direction.

Typically, the halftone phase shift film has a thickness of up to 70 nm.

In a preferred embodiment, the halftone phase shift film has a surfaceroughness RMS of up to 0.6 nm.

In a preferred embodiment, the mask blank further includes a second filmon the halftone phase shift film, the second film being a single layeror a multilayer film composed of a chromium-containing material. Thesecond film may be a light-shielding film, a combination oflight-shielding film and antireflective film, or a processing auxiliaryfilm which functions as a hard mask during pattern formation of thehalftone phase shift film.

In a preferred embodiment, the mask blank further includes a third filmon the second film, the third film being a single layer or a multilayerfilm composed of a silicon-containing material. The second film may be alight-shielding film, a combination of light-shielding film andantireflective film, or a processing auxiliary film which functions as ahard mask during pattern formation of the halftone phase shift film, andthe third film is a processing auxiliary film which functions as a hardmask during pattern formation of the second film. Also the second filmmay be a processing auxiliary film which functions as a hard mask duringpattern formation of the halftone phase shift film and as an etchstopper during pattern formation of the third film, and the third filmis a light-shielding film or a combination of light-shielding film andantireflective film.

In a preferred embodiment, the mask blank further includes a fourth filmon the third film, the fourth film being a single layer or a multilayerfilm composed of a chromium-containing material. Typically, the secondfilm is a processing auxiliary film which functions as a hard maskduring pattern formation of the halftone phase shift film and as an etchstopper during pattern formation of the third film, the third film is alight-shielding film or a combination of light-shielding film andantireflective film, and the fourth film is a processing auxiliary filmwhich functions as a hard mask during pattern formation of the thirdfilm.

Also contemplated herein is a halftone phase shift mask prepared fromthe halftone phase shift mask blank defined above.

Advantageous Effects of Invention

The halftone phase shift mask blank of the invention has a halftonephase shift film which experiences minimal pattern size variationdegradation with respect to light of wavelength up to 200 nm, has goodchemical resistance, and is improved in processability over transitionmetal-free silicon base material films. The inventive halftone phaseshift film is improved in processability over transition metal-freesilicon base material films as demonstrated by a higher etching rateduring fluorine base dry etching than transition metal-free silicon basematerial films, while it maintains substantially equivalent laserirradiation resistance and chemical resistance to transition metal-freesilicon base material films. In addition, the inventive halftone phaseshift film has a low sheet resistance enough to suppress any chargebuildup.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are cross-sectional views of one exemplary halftonephase shift mask blank and halftone phase shift mask of the invention,respectively.

FIGS. 2A, 2B and 2C are cross-sectional views of further embodiments ofthe halftone phase shift mask blank of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention pertains to a halftone phase shift mask blank (or halftonephase shift type photomask blank) comprising a transparent substrate anda halftone phase shift film formed thereon. The transparent substrate istypically a quartz substrate. Preference is given to transparentsubstrates of 6 inch squares and 25 mil thick, known as 6025 substrate,as prescribed in the SEMI standards, or transparent substrates of 152 mmsquares and 6.35 mm thick when expressed in the SI units. The halftonephase shift film may be a single layer structure or a multilayerstructure (i.e., two or more layers). The invention also pertains to ahalftone phase shift (photo)mask having a (photo)mask pattern of ahalftone phase shift film.

FIG. 1A is a cross-sectional view of a halftone phase shift mask blankin one embodiment of the invention. The halftone phase shift mask blank100 includes a transparent substrate 10 and a halftone phase shift film1 formed thereon. FIG. 1B is a cross-sectional view of a halftone phaseshift mask in one embodiment of the invention. The halftone phase shiftmask 101 includes a transparent substrate 10 and a halftone phase shiftfilm pattern 11 thereon.

The halftone phase shift film may be composed of a single layer ormultiple layers as long as a phase shift and a transmittance necessaryfor the halftone phase shift function are met. In the case of multilayerstructure, the film is preferably composed of multiple layers includingan antireflective function layer so that the overall film may meet apredetermined surface reflectance as well as the necessary phase shiftand transmittance.

In either of the single layer and multilayer structure, each layer maybe a compositionally graded layer, i.e., a layer wherein theconcentration of some or all constituent elements varies continuously inthickness direction. In particular, the layer (A) of the predeterminedcomposition to be described later should preferably be a layer whereinthe concentration of some or all constituent elements variescontinuously in thickness direction. In the case of multilayerstructure, the halftone phase shift film may be a combination of two ormore layers selected from layers composed of different constituents andlayers composed of identical constituents in different compositionalratios. Where the film is composed of three or more layers, identicallayers may be included as long as they are not contiguous to each other.

Since halftone phase shift masks are used in the photolithography usingexposure light of wavelength up to 200 nm, typically ArF excimer laserlight (wavelength 193 nm), the halftone phase shift film should providea predetermined phase shift and a predetermined transmittance withrespect to the exposure light at a predetermined thickness.

The overall thickness of the halftone phase shift film should preferablybe up to 70 nm, and more preferably up to 65 nm, because a thinner filmfacilitates to form a finer pattern. The lower limit of the filmthickness is set in the range where the desired optical properties areobtained relative to light of wavelength up to 200 nm. Specifically, thefilm thickness is set at least 40 nm, though the lower limit is notcritical.

The phase shift of the halftone phase shift film with respect toexposure light is such that a phase shift between the exposure lighttransmitted by a region of phase shift film (phase shift region) and theexposure light transmitted by a neighboring region where the phase shiftfilm is removed, causes interference of exposure light at the boundarywhereby contrast is increased. Specifically the phase shift is 150 to200 degrees. Although ordinary halftone phase shift films are set to aphase shift of approximately 180°, it is possible from the standpoint ofcontrast enhancement to adjust the phase shift below or beyond 180°. Forexample, setting a phase shift of smaller than 180° is effective forforming a thinner film. It is a matter of course that a phase shiftcloser to 180° is more effective because a higher contrast is available.In this regard, the phase shift is preferably 160 to 190°, morepreferably 175 to 185°, and most preferably approximately 180°. Also thehalftone phase shift film has a transmittance of exposure light of atleast 3%, preferably at least 5%, and up to 30%.

Preferably the halftone phase shift film has a surface roughness (RMS)of up to 0.6 nm. The surface roughness (RMS) used herein is a surfaceroughness (RMS) as measured by an atomic force microscope (AFM). Asmaller value of surface roughness is preferred in that smaller defectsare detectable upon defect inspection. Also preferably the halftonephase shift film has a sheet resistance of up to 10¹³ ohm/squares (Ω/□),especially up to 10¹² Ω/□. In particular, the layer (A) to be describedbelow should have a sheet resistance of up to 10¹⁵ Ω/□, especially up to10¹³ Ω/□. As long as the sheet resistance of the halftone phase shiftfilm falls in the range, any charge buildup, for example, charge buildupduring the measurement of mask pattern size under electron microscope,typically scanning electron microscope (SEM) can be suppressed, enablingmore accurate size measurement.

While the halftone phase shift film has a phase shift, transmittance andthickness in the above-defined ranges, it preferably has a refractiveindex n of at least 2.4, more preferably at least 2.5, and even morepreferably at least 2.6 with respect to exposure light. By reducing theoxygen content of the halftone phase shift film, preferably byeliminating oxygen, the refractive index n of the film can be increased,and the thickness of the film can be reduced while maintaining thenecessary phase shift for the phase shift function. The refractive indexn is higher as the oxygen content is lower, and in turn, the necessaryphase shift is available from a thinner film as the refractive index nis higher. Therefore, when the halftone phase shift film is a singlelayer structure, this single layer preferably has a refractive index nof at least 2.4, more preferably at least 2.5, and oven more preferablyat least 2.6. When the halftone phase shift film is a multilayerstructure, a portion thereof corresponding to at least 60%, preferablyat least 70%, more preferably at least 80%, further preferably at least90%, most preferably 100% of the overall thickness preferably has arefractive index n of at least 2.4, more preferably at least 2.5, andeven more preferably at least 2.6.

While the halftone phase shift film has a phase shift, transmittance andthickness in the above-defined ranges, it preferably has an extinctioncoefficient k of at least 0.4, especially at least 0.6 and up to 0.7,especially up to 0.65 with respect to exposure light. When the halftonephase shift film is a single layer structure, this single layerpreferably has an extinction coefficient k of at least 0.4, especiallyat least 0.6 and up to 0.7, especially up to 0.65. When the halftonephase shift film is a multilayer structure, a portion thereofcorresponding to at least 60%, preferably at least 70%, more preferablyat least 80%, further preferably at least 90%, most preferably 100% ofthe overall thickness preferably has an extinction coefficient k of atleast 0.1, especially at least 0.2 and up to 0.7, especially up to 0.65.

The halftone phase shift film is composed of a silicon base materialcomprising essentially a transition metal, silicon and nitrogen andoptionally oxygen. The single layer or each of multiple layers by whichthe halftone phase shift film is constructed is composed of a siliconbase material comprising essentially a transition metal, silicon andnitrogen and optionally oxygen. Inclusion of other elements isacceptable as long as they are in impurity amounts. The halftone phaseshift film includes at least one layer (A) of the predeterminedcomposition. When the halftone phase shift film is a single layer, theoverall single layer is layer (A) of the predetermined composition; orwhen the film is a multilayer film, a portion thereof corresponding toat least 50%, preferably at least 60%, more preferably at least 70% ofthe overall thickness (excluding a surface oxidized layer if any) ispreferably layer (A) of the predetermined composition. In the preferredembodiment, layer (A) accounts for at least 80%, more preferably atleast 90%, and most preferably 100% of the overall thickness. When thehalftone phase shift film is a multilayer film, preferably the outermostsurface layer of the film which is disposed remote from the transparentsubstrate is layer (A).

In the halftone phase shift film, the silicon base material of whichlayer (A) is composed should have a transition metal content of up to 3at %, preferably up to 2 at %, more preferably up to 1.5 at % andpreferably at least 0.1 at %, more preferably at least 0.5 at %, evenmore preferably at least 1 at %. In view of the sheet resistance of thehalftone phase shift film, the content of transition metal is preferablyat least 0.1 at %, more preferably at least 0.5 at %, even morepreferably at least 1 at %. For obtaining a satisfactory sheetresistance, the content of transition metal is more preferably more than1 at %, especially at least 1.1 at %. Suitable transition metals includemolybdenum, zirconium, tungsten, titanium, hafnium, chromium andtantalum. Preferably, molybdenum is contained. Most preferably thetransition metal is molybdenum.

In the halftone phase shift film, the silicon base material of whichlayer (A) is composed should have a total content of silicon, nitrogenand oxygen (a total content of silicon and nitrogen if oxygen-free) ofat least 90 at %, preferably at least 95 at %.

In the halftone phase shift film, the silicon base material of whichlayer (A) is composed should have a silicon content of at least 30 at %,preferably at least 40 at %, and up to 70 at %, preferably up to 55 at%. A portion having a silicon content of up to 50 at % should preferablyaccount for at least 10% of the overall thickness of layer (A). Wherethe halftone phase shift film has a low transmittance (e.g., from 3% toless than 20%, specifically from 3% to 12%, more specifically from 3% toless than 10%), the silicon base material preferably has a siliconcontent of at least 40 at %, preferably at least 44 at %, and up to 70at %, preferably up to 55 at %; and a portion having a silicon contentof up to 50 at % should preferably account for at least 10% of theoverall thickness of layer (A). Where the halftone phase shift film hasa high transmittance (e.g., from 20% to 30%), the silicon base materialpreferably has a silicon content of at least 30 at %, preferably atleast 40 at %, and up to 55 at %, preferably up to 50 at %; and aportion having a silicon content of up to 45 at % should preferablyaccount for at least 10% of the overall thickness of layer (A).

In the halftone phase shift film, the silicon base material of whichlayer (A) is composed should have a total content of nitrogen and oxygenof at least 30 at %, preferably at least 45 at % and up to 60 at %,preferably up to 55 at %. A portion having a total content of nitrogenand oxygen of at least 50 at % should preferably account for at least10% of the overall thickness of layer (A).

In the halftone phase shift film, the silicon base material of whichlayer (A) is composed should preferably have a nitrogen content of atleast 10 at %, more preferably at least 40 at % and up to 60 at %, morepreferably up to 55 at %. Where the halftone phase shift film has a lowtransmittance (e.g., from 3% to less than 20%, specifically from 3% to12%, more specifically from 3% to less than 10%), the silicon basematerial preferably has a nitrogen content of at least 40 at %,preferably at least 44 at %, and up to 60 at %, preferably up to 56 at%; and a portion having a nitrogen content of at least 48 at %,especially at least 50 at % should preferably account for at least 10%of the overall thickness of layer (A). Where the halftone phase shiftfilm has a high transmittance (e.g., from 20% to 30%), the silicon basematerial preferably has a nitrogen content of at least 10 at %,preferably at least 40 at %, and up to 60 at %, preferably up to 55 at%.

In the halftone phase shift film, the silicon base material of whichlayer (A) is composed should have an oxygen content of up to 30 at %,more preferably up to 6 at %. Where the halftone phase shift film has ahigh transmittance (e.g., from 20% to 30%), the silicon base materialpreferably has an oxygen content of up to 30 at %, preferably up to 25at %. Where the halftone phase shift film has a low transmittance (e.g.,from 3% to less than 20%, specifically from 3% to 12%, more specificallyfrom 3% to less than 10%), the silicon base material preferably has anoxygen content of up to 6 at %, more preferably up to 3.5 at %, evenmore preferably up to 1 at %.

Suitable silicon base materials include transition metal silicon basematerials, specifically a transition metal silicon base materialconsisting of a transition metal (Me), silicon and nitrogen, i.e.,transition metal silicon nitride (MeSiN) and a transition metal siliconbase material consisting of a transition metal (Me), silicon, nitrogenand oxygen, i.e., transition metal silicon oxynitride (MeSiON).

In order to form the halftone phase shift film as a thin film, a siliconbase material with a lower oxygen content is preferred, with anoxygen-free material being more preferred. From this aspect, thehalftone phase shift film should preferably be composed of anoxygen-free silicon base material.

On fluorine base dry etching, the halftone phase shift film preferablyhas a higher etching rate than the transparent substrate. The halftonephase shift film is further improved in processability when a ratio ofthe etching rate of the film to the etching rate of the substrate ispreferably at least 1.25, more preferably at least 1.3, even morepreferably at least 1.35.

While the halftone phase shift film may be deposited by any well-knownfilm-forming techniques, the sputtering technique is preferred becausefilms of homogeneity are readily deposited. Either DC sputtering or RFsputtering may be employed. The target and sputtering gas may heselected as appropriate depending on the layer construction andcomposition of the film. Suitable targets include a silicon target, asilicon nitride target, and a target containing silicon and siliconnitride, which may contain a transition metal. The contents of nitrogenand oxygen may be adjusted during reactive sputtering by usingnitrogen-containing gas, oxygen-containing gas, ornitrogen/oxygen-containing gas, and optionally carbon-containing gas, asthe reactive gas, and adjusting the flow rate thereof. The reactive gasis, for example, nitrogen gas (N₂ gas), oxygen gas (O₂ gas), or nitrogenoxide gases (N₂O gas, NO gas, NO2 gas). A rare gas such as helium, neonor argon gas may be used as the sputtering gas.

In the embodiment wherein the halftone phase shift film is a multilayerfilm, the film may include a surface oxidized layer as the outermostlayer on the surface side (disposed remote from the substrate) in orderto suppress any alteration in quality of the film. The surface oxidizedlayer may have an oxygen content of at least 20 at %, with even anoxygen content of at least 50 at % being acceptable. The surfaceoxidized layer may be formed by atmospheric or air oxidation or forcedoxidative treatment. Examples of forced oxidative treatment includetreatment of a silicon-based material film with ozone gas or ozonewater, and heating of a film at 300° C. or higher in anoxygen-containing atmosphere, typically oxygen gas atmosphere by ovenheating, lamp annealing or laser heating. The surface oxidized layerpreferably has a thickness of up to 10 nm, more preferably up to 5 nm,and even more preferably up to 3 nm. The oxidized layer exerts itseffect as long as its thickness is at least 1 nm. Although the surfaceoxidized layer may also be formed by increasing the amount of oxygen inthe sputtering gas during the sputtering step, atmospheric oxidation oroxidative treatment as mentioned above is preferred for forming a lessdefective layer.

In the halftone phase shift mask blank of the invention, a second filmof single layer or multilayer structure may be formed on the halftonephase shift film. Most often, the second film is disposed contiguous tothe halftone phase shift film. Examples of the second film include alight-shielding film, a combination of light-shielding film andantireflective film, and a processing auxiliary film which functions asa hard mask during subsequent pattern formation of the halftone phaseshift film. When a third film is formed as will be described later, thesecond film may be utilized as a processing auxiliary film (etching stopfilm) which functions as an etching stopper during subsequent patternformation of the third film. The second film is preferably composed of achromium-containing material.

One exemplary embodiment is a halftone phase shift mask blankillustrated in FIG. 2A. The halftone phase shift mask blank depicted at100 in FIG. 2A includes a transparent substrate 10, a halftone phaseshift film 1 formed on the substrate, and a second film 2 formed on thefilm 1.

The halftone phase shift mask blank may include a light-shielding filmas the second film on the halftone phase shift film. A combination of alight-shielding film and an antireflective film may also be used as thesecond film. The provision of the second film including alight-shielding film ensures that a halftone phase shift mask includes aregion capable of completely shielding exposure light. Thelight-shielding film and antireflective film may also be utilized as aprocessing auxiliary film during etching. The construction and materialof the light-shielding film and antireflective film are known from manypatent documents, for example, Patent Document 4 (JP-A 2007-033469) andPatent Document 5 (JP-A 2007-233179). One preferred film construction ofthe light-shielding film and antireflective film is a structure having alight-shielding film of Cr-containing material and an antireflectivefilm of Cr-containing material for reducing reflection by thelight-shielding film. Each of the light-shielding film and theantireflective film may be a single layer or multilayer. SuitableCr-containing materials of which the light-shielding film andantireflective film are made include chromium alone, chromium oxide(CrO), chromium nitride (CrN), chromium carbide (CrC), chromiumoxynitride (CrON), chromium oxycarbide (CrOC), chromium nitride carbide(CrNC), chromium oxynitride carbide (CrONC) and other chromiumcompounds.

Where the second film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the light-shieldingfilm is made of a chromium base material having a chromium content of atleast 40 at %, especially at least 60 at % and less than 100 at %,preferably up to 99 at %, and more preferably up to 90 at %. Thechromium base material has an oxygen content of at least 0 at % and upto 60 at %, preferably up to 40 at %, with an oxygen content of at least1 at % being preferred when an etching rato must be adjusted. Thechromium base material has a nitrogen content of at least 0 at % and upto 50 at %, preferably up to 40 at %, with a nitrogen content of atleast 1 at % being preferred when an etching rate must be adjusted. Thechromium base material has a carbon content of at least 0 at % and up to20 at %, preferably up to 10 at %, with a carbon content of at least 1at % being preferred when an etching rate must be adjusted. The totalcontent of chromium, oxygen, nitrogen and carbon is preferably at least95 at %, more preferably at least 99 at %, and especially 100 at %.

Where the second film is a combination of a light-shielding film and anantireflective film, the antireflective film is preferably made of achromium-containing material having a chromium content of preferably atleast 30 at %, more preferably at least 35 at % and preferably up to 70at %, and more preferably up to 50 at %. The chromium-containingmaterial preferably has an oxygen content of up to 60 at %, and at least1 at % and more preferably at least 20 at %. The chromium-containingmaterial preferably has a nitrogen content of up to 50 at %, morepreferably up to 30 at %, and at least 1 at %, more preferably at least3 at %. The chromium-containing material preferably has a carbon contentof at least 0 at % and up to 20 at %, more preferably up to 5 at %, witha carbon content of at least 1 at % being preferred when an etching ratemust be adjusted. The total content of chromium, oxygen, nitrogen andcarbon is preferably at least 95 at %, more preferably at least 99 at %,and especially 100 at %.

Where the second film is a processing auxiliary film (etching mask film)which functions as a hard mask during pattern formation of the halftonephase shift film, the processing auxiliary film is preferably composedof a material having different etching properties from the halftonephase shift film, for example, a material having resistance to fluorinedry etching applied to the etching of silicon-containing material,specifically a chromium-containing material which can be etched withoxygen-containing chlorine gas. Suitable chromium-containing materialsinclude chromium alone, chromium oxide (CrO), chromium nitride (CrN),chromium carbide (CrC), chromium oxynitride (CrON), chromium oxycarbide(CrOC), chromium nitride carbide (CrNC), chromium oxynitride carbide(CrONC) and other chromium compounds.

Where the second film is a processing auxiliary film, the filmpreferably has a chromium content of preferably at least 40 at %, morepreferably at least 50 at % and up to 100 at %, more preferably up to 99at %, and even more preferably up to 90 at %. The film has an oxygencontent of at least 0 at %, and up to 60 at %, preferably up to 55 at %,with an oxygen content of at least 1 at % being preferred when anetching rate must be adjusted. The film has a nitrogen content of atleast 0 at %, and up to 50 at %, preferably up to 40 at %, with anitrogen content of at least 1 at % being preferred when an etching ratemust be adjusted. The film has a carbon content of at least 0 at % andup to 20 at %, preferably up to 10 at %, with a carbon content of atleast 1 at % being preferred when an etching rate must be adjusted. Thetotal content of chromium, oxygen, nitrogen and carbon is preferably atleast 95 at %, more preferably at least 99 at %, and especially 100 at%.

Where the second film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the second film has athickness of typically 20 to 100 nm, preferably 40 to 70 nm. Also thehalftone phase shift film combined with the second film shouldpreferably have a total optical density of at least 2.0, more preferablyat least 2.5, and even more preferably at least 3.0, with respect toexposure light of wavelength up to 200 nm. Where the second film is aprocessing auxiliary film, the second film has a thickness of typically1 to 100 nm, preferably 2 to 50 nm.

In the halftone phase shift mask blank of the invention, a third film ofsingle layer or multilayer structure may be formed on the second film.Most often, the third film is disposed contiguous to the second film.Examples of the third film include a light-shielding film, a combinationof light-shielding film and antireflective film, and a processingauxiliary film which functions as a hard mask during subsequent patternformation of the second film. The third film is preferably composed of asilicon-containing material, especially chromium-free silicon-containingmaterial.

One exemplary embodiment is a halftone phase shift mask blankillustrated in FIG. 2B. The halftone phase shift mask blank depicted at100 in FIG. 2B includes a transparent substrate 10, a halftone phaseshift film 1 formed on the substrate, a second film 2 formed on the film1, and a third film 3 formed on the second film 2.

Where the second film is a light-shielding film, a combination of alight-shielding film and an antireflective film or a processingauxiliary film which functions as a hard mask during subsequent patternformation of the halftone phase shift film, the third film may be aprocessing auxiliary film (etching mask film) which functions as a hardmask during subsequent pattern formation of the second film. When afourth film is formod as will be described later, the third film may beutilized as a processing auxiliary film (etching stop film) whichfunctions as an etching stopper during subsequent pattern formation ofthe fourth film. The processing auxiliary film is preferably composed ofa material having different etching properties from the second film, forexample, a material having resistance to chlorine dry etching applied tothe etching of chromium-containing material, specifically asilicon-containing material which can be etched with fluoride gas suchas SF₆ or CF₄. Suitable silicon-containing materials include siliconalone, a material containing silicon and one or both of nitrogen andoxygen, a material containing silicon and a transition metal, and amaterial containing silicon, one or both of nitrogen and oxygen, and atransition metal. Exemplary of the transition metal are molybdenum,tantalum and zirconium.

Where the third film is a processing auxiliary film, it is preferablycomposed of a silicon-containing material having a silicon content ofpreferably at least 20 at %, more preferably at least 33 at % and up to95 at %, more preferably up to 80 at %. The silicon-containing materialhas a nitrogen content of at least 0 at % and up to 50 at %, preferablyup to 30 at %, with a nitrogen content of at least 1 at % beingpreferred when an etching rate must be adjusted. The silicon-containingmaterial has an oxygen content of at least 0 at %, preferably at least20 at % and up to 70 at %, preferably up to 66 at %, with an oxygencontent of at least 1 at % being preferred when an etching rate must beadjusted. The silicon-containing material has a transition metal contentof at least 0 at % and up to 35 at %, preferably up to 20 at %, with atransition metal content of at least 1 at % being preferred if present.The total content of silicon, oxygen, nitrogen and transition metal ispreferably at least 95 at %, more preferably at least 99 at %, andespecially 100 at %.

Where the second film is a light-shielding film or a combination of alight-shielding film and an antireflective film and the third film is aprocessing auxiliary film, the second film has a thickness of typically20 to 100 nm, preferably 40 to 70 nm, and the third film has a thicknessof typically 1 to 30 nm, preferably 2 to 15 nm. Also the halftone phaseshift film combined with the second film should preferably have a totaloptical density of at least 2.0, more preferably at least 2.5, and evenmore preferably at least 3.0, with respect to exposure light ofwavelength up to 200 nm. Where the second film is a processing auxiliaryfilm and the third film is a processing auxiliary film, the second filmhas a thickness of typically 1 to 100 nm, preferably 2 to 50 nm, and thethird film has a thickness of typically 1 to 30 nm, preferably 2 to 15nm.

Where the second film is a processing auxiliary film, a light-shieldingfilm may be formed as the third film. Also, a combination of alight-shielding film and an antireflective film may be formed as thethird film. Herein the second film may be utilized as a processingauxiliary film (etching mask film) which functions as a hard mask duringpattern formation of the halftone phase shift film, or a processingauxiliary film (etching stop film) which functions as an etching stopperduring pattern formation of the third film. Examples of the processingauxiliary film are films of chromium-containing materials as describedin Patent Document 6 (JP-A 2007-241065). The processing auxiliary filmmay be a single layer or multilayer. Suitable chromium-containingmaterials of which the processing auxiliary film is made includechromium alone, chromium oxide (CrO), chromium nitride (CrN), chromiumcarbide (CrC), chromium oxynitride (CrON), chromium oxycarbide (CrOC),chromium nitride carbide (CrNC), chromium oxynitride carbide (CrONC) andother chromium compounds.

Where the second film is a processing auxiliary film, the filmpreferably has a chromium content of preferably at least 40 at %, morepreferably at least 50 at % and up to 100 at %, more preferably up to 99at %, and even more preferably up to 90 at %. The film has an oxygencontent of at least 0 at %, and up to 60 at %, preferably up to 55 at %,with an oxygen content of at least 1 at % being preferred when anetching rate must be adjusted. The film has a nitrogen content of atleast 0 at %, and up to 50 at %, preferably up to 40 at %, with anitrogen content of at least 1 at % being preferred when an etching ratemust be adjusted. The film has a carbon content of at least 0 at % andup to 20 at %, preferably up to 10 at %, with a carbon content of atleast 1 at % being preferred when an etching rate must be adjusted. Thetotal content of chromium, oxygen, nitrogen and carbon is preferably atleast 95 at %, more preferably at least 99 at %, and especially 100 at%.

On the other hand, the light-shielding film and antireflective film asthe third film are preferably composed of a material having differentetching properties from the second film, for example, a material havingresistance to chlorine dry etching applied to the etching ofchromium-containing material, specifically a silicon-containing materialwhich can be etched with fluoride gas such as SF₆ or CF₄. Suitablesilicon-containing materials include silicon alone, a materialcontaining silicon and nitrogen and/or oxygen, a material containingsilicon and a transition metal, and a material containing silicon,nitrogen and/or oxygen, and a transition metal. Exemplary of thetransition metal are molybdenum, tantalum and zirconium.

Where the third film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the light-shieldingfilm and antirefleclive film are preferably composed of asilicon-containing material having a silicon content of preferably atleast 10 at %, more preferably at least 30 at % and less than 100 at %,more preferably up to 95 at %. The silicon-containing material has anitrogen content of at least 0 at % and up to 50 at %, preferably up to40 at %, especially up to 20 at %, with a nitrogen content of at least 1at % being preferred when an etching rate must be adjusted. Thesilicon-containing material has an oxygen content of at least 0 at %,and up to 60 at %, preferably up to 30 at %, with an oxygen content ofat least 1 at % being preferred when an etching rate must be adjusted.The silicon-containing material has a transition metal content of atleast 0 at % and up to 35 at %, preferably up to 20 at %, with atransition metal content of at least 1 at % being preferred if present.The total content of silicon, oxygen, nitrogen and transition metal ispreferably at least 95 at %, more preferably at least 99 at %, andespecially 100 at %.

Where the second film is a processing auxiliary film and the third filmis a light-shielding film or a combination of a light-shielding film andan antireflective film, the second film has a thickness of typically 1to 20 nm, preferably 2 to 10 nm, and the third film has a thickness oftypically 20 to 100 nm, preferably 30 to 70 nm. Also the halftone phaseshift film combined with the second and third films should preferablyhave a total optical density of at least 2.0, more preferably at least2.5, and even more preferably at least 3.0, with respect to exposurelight of wavelength up to 200 nm.

In the halftone phase shift photomask blank of the invention, a fourthfilm of single layer or multilayer structure may be formed on the thirdfilm. Most often, the fourth film is disposed contiguous to the thirdfilm. Exemplary of the fourth film is a processing auxiliary film whichfunctions as a hard mask during subsequent pattern formation of thethird film. The fourth film is preferably composed of achromium-containing material.

One exemplary embodiment is a halftone phase shift mask blankillustrated in FIG. 2C. The halftone phase shift mask blank depicted at100 in FIG. 2C includes a transparent substrate 10, a halftone phaseshift film 1 formed on the substrate, a second film 2 formed on the film1, a third film 3 formed on the second film 2, and a fourth film 4formed on the third film 3.

Where the third film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the fourth film may bea processing auxiliary film (etching mask film) which functions as ahard mask during subsequent pattern formation of the third film. Theprocessing auxiliary film is preferably composed of a material havingdifferent etching properties from the third film, for example, amaterial having resistance to fluorine dry etching applied to theetching of silicon-containing material, specifically achromium-containing material which can be etched with oxygen-containingchloride gas. Suitable chromium-containing materials include chromiumalone, chromium oxide (CrO), chromium nitride (CrN), chromium carbide(CrC), chromium oxynitride (CrON), chromium oxycarbide (CrOC), chromiumnitride carbide (CrNC), chromium oxynitride carbide (CrONC) and otherchromium compounds.

Where the fourth film is a processing auxiliary film, the film has achromium content of at least 40 at %, preferably at least 50 at % and upto 100 at %, preferably up to 99 at %, and more preferably up to 90 at%. The film has an oxygen content of at least 0 at % and up to 60 at %,preferably up to 40 at %, with an oxygen content of at least 1 at %being preferred when an etching rate must be adjusted. The film has anitrogen content of at least 0 at % and up to 50 at %, preferably up to40 at %, with a nitrogen content of at least 1 at % being preferred whenan etching rate must be adjusted. The film has a carbon content of atleast 0 at % and up to 20 at %, preferably up to 10 at %, with a carboncontent of at least 1 at % being preferred when an etching rate must beadjusted. The total content of chromium, oxygen, nitrogen and carbon ispreferably at least 95 at %, more preferably at least 99 at %, andespecially 100 at %.

Where the second film is a processing auxiliary film, the third film isa light-shielding film or a combination of a light-shielding film and anantireflective film, and the fourth film is a processing auxiliary film;the second film has a thickness of typically 1 to 20 nm, preferably 2 to10 nm, the third film has a thickness of typically 20 to 100 nm,preferably 30 to 70 nm, and the fourth film has a thickness of typically1 to 30 nm, preferably 2 to 20 nm. Also the halftone phase shift filmcombined with the second and third films should preferably have a totaloptical density of at least 2.0, more preferably at least 2.5, and evenmore preferably at least 3.0, with respect to exposure light ofwavelength up to 700 nm.

The second and fourth films of chromium-containing materials may bedeposited by reactive sputtering using a chromium target or a chromiumtarget having one or more of oxygen, nitrogen and carbon added thereto,and a sputtering gas based on a rare gas such as Ar, He or Ne, to whicha reactive gas selected from oxygen-containing gas, nitrogen-containinggas and carbon-containing gas is added depending on the desiredcomposition of a film to be deposited.

The third film of silicon-containing material may be deposited byreactive sputtering using a silicon target, silicon nitride target,target containing silicon and silicon nitride, transition metal target,or composite silicon/transition metal target, and a sputtering gas basedon a rare gas such as Ar, He or Ne, to which a reactive gas selectedfrom oxygen-containing gas, nitrogen-containing gas andcarbon-containing gas is added depending on the desired composition of afilm to be deposited.

The mask blank may be processed into a mask by a standard technique. Forexample, a halftone phase shift mask blank comprising a halftone phaseshift film and a second film of chromium-containing material depositedthereon may be processed as follows. First, a resist film adapted forelectron beam (EB) lithography is formed on the second film of thehalftone phase shift mask blank, exposed to a pattern of EB, anddeveloped in a conventional way, forming a resist pattern. While theresist pattern thus obtained is used as etching mask, oxygen-containingchlorine base dry etching is carried out for transferring the resistpattern to the second film, obtaining a pattern of the second film.Next, while the second film pattern is used as etching mask, fluorinebase dry etching is carried out for transferring the pattern to thehalftone phase shift film, obtaining a pattern of the halftone phaseshift film. If any region of the second film is to be left, a resistpattern for protecting that region is formed on the second film.Thereafter, the portion of the second film which is not protected withthe resist pattern is removed by oxygen-containing chlorine base dryetching. The resist pattern is removed in a conventional manner,yielding a halftone phase shift mask.

In another example, a halftone phase shift mask blank comprising ahalftone phase shift film, a light-shielding film or a light-shieldingfilm/antireflective film of chromium-containing material depositedthereon as a second film, and a processing auxiliary film ofsilicon-containing material deposited thereon as a third film may beprocessed as follows. First, a resist film adapted for EB lithography isformed on the third film of the halftone phase shift mask blank, exposedto a pattern of EB, and developed in a conventional way, forming aresist pattern. While the resist pattern thus obtained is used asetching mask, fluorine base dry etching is carried out for transferringthe resist pattern to the third film, obtaining a pattern of the thirdfilm. While the third film pattern thus obtained is used as etchingmask, oxygen-containing chlorine base dry etching is carried out fortransferring the third film pattern to the second film, obtaining apattern of the second film. The resist pattern is removed at this point.Further, while the second film pattern is used as etching mask, fluorinebase dry etching is carried out for transferring the second film patternto the halftone phase shift film to define a pattern of the halftonephase shift film and at the same time, removing the third film pattern.If any region of the second film is to be left, a resist pattern forprotecting that region is formed on the second film. Thereafter, theportion of the second film which is not protected with the resistpattern is removed by oxygen-containing chlorine base dry etching. Theresist pattern is removed in a conventional manner, yielding a halftonephase shift mask.

In a further example, a halftone phase shift mask blank comprising ahalftone phase shift film, a processing auxiliary film ofchromium-containing material deposited thereon as a second film, and alight-shielding film or a light-shielding film/antireflective film ofsilicon-containing material deposited on the second film as a third filmmay be processed as follows. First, a resist film adapted for EBlithography is formed on the third film of the halftone phase shift maskblank, exposed to a pattern of EB, and developed in a conventional way,forming a resist pattern. While the resist pattern thus obtained is usedas etching mask, fluorine base dry etching is carried out fortransferring the resist pattern to the third film, obtaining a patternof the third film. While the third film pattern thus obtained is used asetching mask, oxygen-containing chlorine base dry etching is carried outfor transferring the third film pattern to the second film, whereby apattern of the second film is obtained, that is, a portion of the secondfilm where the halftone phase shift film is to be removed is removed.The resist pattern is removed at this point. A resist pattern forprotecting a portion of the third film to be left is formed on the thirdfilm. Further, while the second film pattern is used as etching mask,fluorine base dry etching is carried out for transferring the secondfilm pattern to the halftone phase shift film to define a pattern of thehalftone phase shift film and at the same time, removing the portion ofthe third film which is not protected with the resist pattern. Theresist pattern is removed in a conventional manner. Finally,oxygen-containing chlorine base dry etching is carried out to remove theportion of the second film where the third film has been removed,yielding a halftone phase shift mask.

In a still further example, a halftone phase shift mask blank comprisinga halftone phase shift film, a processing auxiliary film ofchromium-containing material deposited thereon as a second film, alight-shielding film or a light-shielding film/antireflective film ofsilicon-containing material deposited on the second film as a thirdfilm, and a processing auxiliary film of chromium-containing materialdeposited on the third film as a fourth film may be processed asfollows. First, a resist film adapted for EB lithography is formed onthe fourth film of the halftone phase shift mask blank, exposed to apattern of EB, and developed in a conventional way, forming a resistpattern. While the resist pattern thus obtained is used as etching mask,oxygen-containing chlorine base dry etching is carried out fortransferring the resist pattern to the fourth film, obtaining a patternof the fourth film. While the fourth film pattern thus obtained is usedas etching mask, fluorine base dry etching is carried out fortransferring the fourth film pattern to the third film, obtaining apattern of the third film. The resist pattern is removed at this point.A resist pattern for protecting a portion of the third film to be leftis formed on the fourth film. Further, while the third film pattern isused as etching mask, oxygen-containing chlorine base dry etching iscarried out for transferring the third film pattern to the second film,obtaining a pattern of the second film and at the same time, removingthe portion of the fourth film which is not protected with the resistpattern. Next, while the second film pattern is used as etching mask,fluorine base dry etching is carried out for transferring the secondfilm pattern to the halftone phase shift film to define a pattern of thehalftone phase shift film and at the same time, removing the portion ofthe third film which is not protected with the resist pattern. Theresist pattern is removed in a conventional manner. Finally,oxygen-containing chlorine base dry etching is carried out to remove theportion of the second film where the third film has been removed and theportion of the fourth film where the resist pattern has been removed,yielding a halftone phase shift mask.

In a photolithographic method for forming a pattern with a half pitch ofup to 50 nm, typically up to 30 nm, and more typically up to 20 nm on aprocessable substrate, comprising the steps of forming a photoresistfilm on the processable substrate and exposing the photoresist film tolight of wavelength up to 200 nm, typically ArF excirner laser (193 nm)or F₂ laser (157 nm), through a patterned mask for transferring thepattern to the photoresist film, the halftone phase shift mask of theinvention is best suited for use in the exposure step.

EXAMPLE

Examples are given below for further illustrating the invention althoughthe invention is not limited thereto.

Example 1

A DC magnetron sputtering system capable of simultaneously inducingelectric discharge to two targets was loaded with a MoSi target and a Sitarget. A quartz substrate of 152 mm squares and 6.35 mm thick was setin the chamber. Sputtering was carried out by applying a power of 35 Wacross the MoSi target and a power of 1,900 W across the Si target forsimultaneous discharge, feeding Ar gas and N₂ gas as the sputtering gas,adjusting the flow rate of Ar gas constant at 21 sccm, and continuouslyvarying the flow rate of N₂ gas from 26 sccm to 47 sccm. A halftonephase shift film of MoSiN was deposited on the quartz substrate. Thefilm had a composition that was continuously graded in thicknessdirection, a phase shift of 179° and a transmittance of 6% with respectto light of wavelength 193 nm, and a thickness of 65 nm. In this way, ahalftone phase shift mask blank was obtained.

The halftone phase shift film was analyzed for composition by X-rayphotoelectron spectroscopy (XPS), finding that the contents of Mo and Ncontinuously decreased, and the content of silicon continuouslyincreased in thickness direction. The film composition on the substrateside was Mo:Si:N=1.4:46.5:52.1 (atomic ratio), and the film compositionon the surface side (remote from the substrate) wasMo:Si:N=0.9:52.3:46.8 (atomic ratio). The thickness of a portion havinga Mo content in excess of 1.1 at % accounted for 50% of the overallthickness of the halftone phase shift film.

The halftone phase shift film had a surface roughness (RMS) of 0.51 nmas measured under AFM and a sheet resistance of 10¹² Ω/□. On fluorinebase dry etching with SF₆ gas and O₂ gas, the film had an etching rateof 0.76 nm/sec, which was 1.43 times the etching rate (0.53 nm/sec) ofquartz substrate under the same conditions. The fluorine base dryetching was performed in an etching system having two high-frequencypower supplies, by assigning reactive ion etching by continuousdischarge at 54 W to one power supply and inductively coupled plasma bycontinuous discharge at 325 W to the other power supply, and feeding SF₆gas at a flow rate of 18 sccm and O₂ gas at a flow rate of 45 sccm.

The halftone phase shift film was evaluated for chemical resistance byimmersing the film in AMP (30 wt % aqueous ammonia:30 wt % aqueoushydrogen peroxide:deionized water=1:1:200 in volume ratio) for 120minutes. Chemical resistance was satisfactory as demonstrated by a phaseshift change of 0° after chemical treatment (phase shift unchanged). Bythe standard technique, the halftone phase shift film was processed toform a mask pattern having a line width of 200 nm, yielding a halftonephase shift mask. In air at room temperature (23° C.) and relativehumidity 45%, the mask pattern was irradiated with ArF excimer laserpulses to a cumulative dose of 40 kJ/cm², finding that the mask patternline width experienced a change of 1 nm or less, that is, substantiallyunchanged. The film was minimized in pattern size variation.

Comparative Example 1

The same sputtering system as in Example 1 was loaded with only a Sitarget. A quartz substrate of 152 mm squares and 6.35 mm thick was setin the chamber. Sputtering was carried out by applying a power of 1,900W across the Si target for discharge, feeding Ar gas and N₂ gas as thesputtering gas, adjusting the flow rate of Ar gas constant at 22 sccm,and continuously varying the flow rate of N₂ gas from 23.5 sccm to 44.5sccm. A halftone phase shift film of SiN was deposited on the quartzsubstrate. The film had a composition that was continuously graded inthickness direction, a phase shift of 179° and a transmittance of 6%with respect to light of wavelength 193 nm, and a thickness of 64 nm. Inthis way, a halftone phase shift mask blank was obtained.

The halftone phase shift film had a surface roughness (RMS) of 0.51 nmas measured under AFM and a sheet resistance in excess of themeasurement limit: 10¹³ Ω/□. In the etching test as in Example 1, thefilm had an etching rate of 0.65 nm/sec, which was 1.23 times theetching rate of quartz substrate. In the chemical test as in Example 1,chemical resistance was satisfactory as demonstrated by a phase shiftchange of 0° after chemical treatment (phase shift unchanged). In thelaser irradiation test as in Example 1, the mask pattern line widthexperienced a change of 1 nm or less, that is, substantially unchanged.The film was minimized in pattern size variation.

Comparative Example 2

The same sputtering system as in Example 1 was loaded with a MoSi targetand a Si target. A quartz substrate of 152 mm squares and 6.35 mm thickwas set in the chamber. Sputtering was carried out by applying a powerof 725 W across the MoSi target and a power of 1,275 W across the Sitarget for simultaneous discharge, feeding Ar gas, N₂ gas and O₂ gas asthe sputtering gas, adjusting the flow rate of Ar gas constant at 8.5sccm, the flow rate of N₂ gas constant at 65 sccm, and the flow rate ofO₂ gas constant at 2.6 sccm. A halftone phase shift film of MoSiON wasdeposited on the quartz substrate. The film had a composition that wasconstant in thickness direction, a phase shift of 177° and atransmittance of 6% with respect to light of wavelength 193 nm, and athickness of 75 nm. In this way, a halftone phase shift mask blank wasobtained.

On XPS analysis, the halftone phase shift film had a composition ofMo:Si:N:O=8.7:36.1:45.1:10.1 (atomic ratio). The film had a surfaceroughness (RMS) of 0.75 nm as measured under AFM. In the laserirradiation test as in Example 1, the mask pattern line widthexperienced a large change of 26.7 nm. The film was poor in pattern sizevariation.

Japanese Patent Application No. 2016-190050 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A halftone phase shift mask blank comprising a transparent substrate and a halftone phase shift film thereon having a phase shift of 150° to 200° and a transmittance of 3% to 30% with respect to light of wavelength up to 200 nm, wherein said halftone phase shift film is a single layer or a multilayer film, and is composed of a silicon base material comprising essentially a transition metal, silicon and nitrogen and optionally oxygen, said halftone phase shift film includes at least one layer (A) composed of a silicon base material having a transition metal content of up to 3 at %, a total content of silicon, nitrogen and oxygen of at least 90 at %, a silicon content of 30 to 70 at %, a total content of nitrogen and oxygen of 30 to 60 at %, and an oxygen content of up to 30 at %, and having a sheet resistance of up to 10¹³ Ω/□.
 2. The mask blank of claim 1 wherein the transition metal contains molybdenum.
 3. The mask blank of claim 1 wherein the layer (A) is compositionally graded such that the concentration of some or all constituent elements continuously varies in thickness direction.
 4. The mask blank of claim 1 wherein said halftone phase shift film has a thickness of up to 70 nm.
 5. The mask blank of claim 1 wherein said halftone phase shift film has a surface roughness RMS of up to 0.6 nm.
 6. The mask blank of claim 1, further comprising a second film on said halftone phase shift film, the second film being a single layer or a multilayer film composed of a chromium-containing material.
 7. The mask blank of claim 6 wherein the second film is a light-shielding film, a combination of light-shielding film and antireflective film, or a processing auxiliary film which functions as a hard mask during pattern formation of the halftone phase shift film.
 8. The mask blank of claim 6, further comprising a third film on the second film, the third film being a single layer or a multilayer film composed of a silicon-containing material.
 9. The mask blank of claim 8 wherein the second film is a light-shielding film, a combination of light-shielding film and antireflective film, or a processing auxiliary film which functions as a hard mask during pattern formation of the halftone phase shift film, and the third film is a processing auxiliary film which functions as a hard mask during pattern formation of the second film.
 10. The mask blank of claim 8 wherein the second film is a processing auxiliary film which functions as a hard mask during pattern formation of the halftone phase shift film and as an etch stopper during pattern formation of the third film, and the third film is a light-shielding film or a combination of light-shielding film and antireflective film.
 11. The mask blank of claim 8, further comprising a fourth film on the third film, the fourth film being a single layer or a multilayer film composed of a chromium-containing material.
 12. The mask blank of claim 11 wherein the second film is a processing auxiliary film which functions as a hard mask during pattern formation of the halftone phase shift film and as an etch stopper during pattern formation of the third film, the third film is a light-shielding film or a combination of light-shielding film and antireflective film, and the fourth film is a processing auxiliary film which functions as a hard mask during pattern formation of the third film.
 13. A halftone phase shift mask prepared from the halftone phase shift mask blank of claim
 1. 